The delta variant is causing a new wave: are our vaccines still working?

We’re so tired… of the never ending waves of COVID-19, of the public health restrictions. We want our old lives back. Those at the forefront of the response are the most exhausted. Healthcare workers are having to witness and deal with the increasing stream of COVID-19 patients, when we had started hoping that this would be over in the near future.

The next COVID-19 wave is here. We hoped it could be avoided. We hoped the vaccines would stop the spread. Yet cases are rising worldwide, in some cases topping previous records of daily case counts, including in countries with high levels of vaccination. So what is happening? Are the vaccines not working? Why can’t we seem to control this virus? 

Let’s break it down. We’ll start with the bad news, but read on because there is plenty of good news too.

The bad news

The delta variant – a much more transmissible variant – is fuelling this new wave. 

In countries with strong sequencing programs in place, we are seeing that the majority of new cases (over 80% in the US), are due to the delta variant. This variant has been shown to be more transmissible than the original one, and even than the previous variants (alpha, beta and gamma). How much more transmissible? Over two times as much. This means that if a person infected with the original strain could transmit the virus to 2 people on average, a person infected with the delta variant will transmit it to 4-5 people instead. After a few rounds of infection, the difference between the two is huge (see image below). In most places, this high transmissibility of the delta variant is what is fuelling the rise of cases.

Vaccinated people can acquire and transmit the delta variant, even if they don’t get sick

Initial recommendations for fully vaccinated people stating that vaccinated people could drop many of the restrictions were written before the rise of the delta variant.  These recommendations were based on data showing that when vaccinated people did get infected with previous variants (so called breakthrough infections), they had less virus in their bodies (see here and here), and transmission from vaccinated people to others was minimal

Unfortunately, this does not seem to hold true for the delta variant. First, some preliminary studies suggest that the delta variant can lead to more breakthrough infections (infections in fully vaccinated people), than previous variants. Second, early studies show that vaccinated people who get infected with the delta variant have high amounts of virus in their bodies. although it seems like vaccinated people will have the virus in their bodies for a shorter period. And third, initial reports suggest that vaccinated people infected with the delta variant can transmit the virus to others

This changes the approach to public health recommendations, as we now need to consider that fully vaccinated people may transmit the virus.

The delta variant may cause more severe disease – still to be confirmed

Some reports have suggested that delta can cause more severe disease, including a higher risk of requiring oxygen, of being admitted to the intensive care unit and of death. Comparing severity of the disease from the delta variant versus other variants is challenging though, as the higher transmissibility of the virus might bias the number and type of people infected. Also, since delta took over so fast, it is almost impossible to carry out studies with people infected at the same time in the same place/hospital, with different variants. Thus, studies have a lot of limitations and need to be taken cautiously until more data is available. 

The good news

This is all highly concerning and discouraging. But what about vaccines? Do they still work against the delta variant? Will they hold the virus at bay? Let’s move on to the good news:

The majority of cases are occurring in people who have not been vaccinated

The vaccines ARE working. Vaccine effectiveness for an infection and symptoms with Delta variant, as reported in preliminary studies in the UK is over 85% for the mRNA vaccines (Pfizer and Moderna) and somewhat lower (67-77%) for AstraZeneca.The majority of cases in this delta-fuelled wave are still happening in unvaccinated people. 

In low and middle income countries which have had very little access to vaccine doses, the people developing severe symptoms are similar to what has been seen in previous waves: older people and/or people with other diseases and conditions. 

In high income countries where vaccines have been readily available, the unvaccinated today are a mix of many younger people who are not yet eligible for vaccination, a smaller proportion of people who cannot get vaccinated due to health reasons, plus those who have chosen not to get vaccinated. The majority of cases are happening among this unvaccinated fraction of the population. Thus, we are seeing a rise in cases in younger people because there are fewer amongst them who have been vaccinated. 

The vaccines are preventing severe cases, hospitalizations and deaths also in delta variant infections.

If vaccinated people are having milder or asymptomatic infections, this may mean that we are missing more cases among the vaccinated than the unvaccinated and the number of cases in people vaccinated might be somewhat higher than what is being detected. But ultimately, what we care most about is severe disease which carries a risk of hospitalization and deaths, and the numbers for these are quite clear: the protection against severe disease from delta variants conferred by the vaccines in fully vaccinated people remains at 93 to 100% for people vaccinated with the mRNA (Pfizer or Moderna) or the AstraZeneca vaccines in preliminary studies in the US and UK. 

Hospitalizations and deaths among those vaccinated have mostly occurred in people with compromised immune systems, older individuals and those with other chronic conditions (diabetes, heart diseases, obesity, etc).

Face masks, physical distancing and other public health measures still work against the delta variant.

While it is highly reassuring to note that the vaccines strongly protect against severe disease from the delta variant, relying on vaccination alone is not enough. Vaccinated people can transmit the delta variant (and thus put at risk those not yet able to get vaccinated) and 5-10% of hospitalizations  are happening among vaccinated people. 

The good news, however, is that all the other measures that we were using before vaccines became more available: face masks, physical distancing, avoiding large groups of people, frequent hand disinfection, still work very well against the delta variant. We need to go back to using layers of protection. The vaccines have become one of those layers, perhaps the strongest one. Remember the swiss cheese model presented by australian virologist Ian M Mackay a while back: each layer stops some but not all of the virus, by adding more layers, we increase our protection. 

What does this mean for me and my family?

Recommendations vary depending on whether there is high, medium or low transmission in a community, and what the vaccination status of most of the population in that community is, so always refer to your local guidelines. In general, however in areas with medium to high transmission:

If you are fully vaccinated, the risk for yourself of severe disease from a potential delta variant infection is very low, although not zero. As before, people over 60 and those with other conditions need to be especially vigilant. What we need to remember is that while the risk is low for those of us lucky enough to be vaccinated, we may transmit the variant to others, especially those unvaccinated around us (for example children and young people) and those with compromised immune systems. 

To protect our loved ones, it helps to restrict the amount of exposure to other people whose vaccination status we don’t know. When in doubt, wear a mask, avoid contact and practice physical distancing. If you think you may have been exposed, test yourself even if you are fully vaccinated and have no symptoms, and quarantine until you know the results. 

If you are not vaccinated: If you have access to vaccines, then the best course of action is to get vaccinated as soon as possible. If you don’t have access to vaccines, tight public health measures are the best recommendation to protect yourself and others. Avoid crowded settings, use tightly fitting face masks in indoor (and crowded outdoor) settings, maintain physical distance and avoid contact, wash hands often and test yourself in case of potential exposure. 

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