Yesterday the world was given great news. This was perhaps the most positive pieces of news since the pandemic began. Understandably government figures over here in the UK were trying to manage expectations and explain that more information is needed and there are some more steps before we an roll out a mass vaccination program. I liked that they stressed that the MHRA and only the MHRA (our equivalent of the FDA or EMA) would decide whether the balance of benefits and risks were sufficient to grant an emergency authorisation. This crucial decision and the way the vaccine will be prioritised are independent, non political decisions here in the UK as they have always been previously in the USA and around Europe.

What does news mean?

The best source for as much detail as has been revealed is Pfizer’s press release. In my experience even when you work in the company unless you are part of a very tight group you do not get any more news than is released in these press releases.

90% reduction in the risk of catching COVID19 in the vaccinated group of patients. – Pfizer

This headline result is about the best we could possibly hope for. It is unrealistic to expect a vaccine would prevent infection in every single patient. Most vaccines have a risk reduction rate much less than this. In fact the FDA said they were looking for a minimum of a 50% reduction in risk to approve a potential vaccine.

43,538 participants were randomised 50/50 to receive the vaccine or a control. Of the whole group just 94 have confirmed COVID19 so far. The way this is distributed meant that the risk in the vaccinated was less than 10% of the risk in the non-vaccinated. This must mean that around 8 people out of over 20,000 given the vaccine have got COVID19 whilst around 86 in the non vaccinated did. If my educated guess is correct then that would give you approximately 91% risk reduction.

This will not be the final risk estimate

Because patients will continue to be followed and infections will continue to arise some will happen in vaccinated and some in non-vaccinated. Some of the variation will be due to chance. Since this is the first estimate whilst we can be very confident there has been a great response to the vaccine, we cannot be sure that the rate will remain at 90%. Depending on how the rest of the study goes do not be surprised or disappointed if the rate drops a bit. Scientists talk about the confidence intervals around such an estimate. At the moment these are likely to be fairly large. They do not disclose what they are but it wouldn’t surprise me if the true result could be anywhere from say 60% to 99%. But this is quibbling over details, the great news is these results are so robust that it must surely make it impossible that the real risk reduction is not well about the 50% the FDA was hoping for.

Over time we will also learn whether those patients who do still catch COVID19 despite having had a vaccine are more likely to have mild disease than those who catch it without having had a vaccine. We will also learn whether a group of patients who had previously had COVID19 are further protected by being vaccinated.

We need more safety data

The FDA has mandated that the safety data should be examined when at least 50% of the participants have been followed up for two months after vaccination. So far there are no safety concerns. And the estimate is that this safety analysis will be complete in just a few weeks.

Manufacture and Distribution

In addition to satisfying regulators on efficacy and safety Pfizer must show that they can manufacture and distribute this to a safe standard. This particular type of vaccine requires a -80C (-112F) storage which is going to pose some significant challenges since very few hospitals let alone Doctor’s surgeries will have the kind of freezer needed!

What this means for other vaccines

Most of the other vaccines under development work in a similar way – i.e. presenting the body with the spoke protein from the virus. Since we already know many of them also produce antibody and T cell response it is reasonable to hope that this news suggests that they too may prove to be effective.

In the case of the Oxford vaccine it similarly presents RNA to the body but does so in a different way which is thought to be more reliable so we do hope that these results increase the likihood this will work too.

The Oxford/Astra Zeneca vaccine is also easier to transport as it merely needs to be refrigerated not frozen and it seems that they are further on with manufacturing and are likely to be able to produce hundreds of millions of doses in a matter of months.

What we already knew

Prior to yesterday we did not know much about immunity and Covid19. We knew that people who are infected produce antibodies and a T cell response. We knew that the antibody response was often short-lived. We suspected but did not know for sure that having antibodies probably protects you against re-infection at least to some degree and for some months. We hoped that the ability to remember how to produce antibodies might not be lost, and that the T cell memory would also reduce the likelihood of someone catching COVID19 for a second time.

We did not know, and still do not know, whether the loss of the antibody response might mean that someone became vulnerable to re-infection six months or more after their first infection. As we are now more than six months after the first wave hit most Western countries we wait with bated breath to learn whether a second infection is rare (we know it can happen already) or whether it becomes very common. We also do not know whether someone who might be protected against getting a severe infection second time round but might be able to pick up the virus and pass it on with an asymptomatic case. This would obviously be concerning for those of us with blood cancer as it would mean that even a family member who you knew had previously been infected would pose a risk to you since the next time round they might not know they were exposing you to the virus.

We also already hoped that antibodies to COVID19 helped through convalescent plasma, although we still do not have proper clinical data to confirm that actually helps since RCTs were not done, with the USA doctors preferring instead to give plasma to anyone they thought might benefit.

Finally, we knew that several of the vaccines currently being studied produce antibodies and T cell responses. Unlike Russia and China, we did not feel that was sufficient. What we really want to know is do vaccines prevent infection with COVID19, and for those who do still get an infection is their disease more mild?

What about blood cancer patients

Most of the vaccines are not live so should not pose a risk to us, but since some blood cancer patients do not have good immune systems what we do not know yet is whether these vaccines will work for us. If they work in the population, however, and produce a shield for us, eradicating the spread of the disease that will be enough for us to be protected. If there will remain a background incidence some of us will need to rely on IVIG or other ways of being immune.

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