The Government announced results from two new vaccine studies from Public Health England (PHE) yesterday. One looked at how much protection the vaccines offer against death once a person is infected, the other at how much protection against hospitalisation with COVID-19 the vaccines offer.
The study on deaths is the more straightforward of the two. It looked at PCR positive cases in England between December 8th and April 6th. It found among 80+ year-olds: 16.1% (1,462/9,105) of unvaccinated cases died versus 9.2% (99/1,072) of cases at least 21 days after their first Pfizer dose, 11.3% (33/293) of cases at least 21 days after their first AstraZeneca dose and 4.7% (6/128) of cases at least seven days after their second Pfizer dose. These correspond to unadjusted relative risk reductions of 43% (Pfizer 1), 30% (AZ 1) and 71% (Pfizer 2) respectively.
Among 70-79 year-olds it found 4.0% (1,147/28,875) of unvaccinated cases died versus 2.7% (15/549) for Pfizer 1, 2.1% (10/484) for AZ 1 and 0% (0/7) for Pfizer 2. This corresponds to unadjusted relative risk reductions of 33% (Pfizer 1), 47% (AZ 1) and 100% (Pfizer 2).
Once adjusted for sex, clinical risk factors, age and being a care home resident, these became relative risk reductions of 44% (Pfizer 1), 55% (AZ 1) and 69% (Pfizer 2). This level of reduction in the mortality rate among the vaccinated over-70s once infected is encouraging. The lack of data on deaths within 21 days of the first jab and seven days of the second jab is disappointing. Why do we have yet another study on vaccine efficacy with no accompanying analysis of safety?
The second study looked at whether vaccination protects against hospitalisation. Unlike the first study, it didn’t look at those already infected (testing positive) to see whether they were hospitalised, but at those who were hospitalised to see whether they’d been vaccinated. It analysed 13,907 admissions in trusts participating in a surveillance programme between December 8th and April 18th. It excluded those who caught the virus in hospital. It also excluded those whose positive PCR test was more than five days before admission (1,230 cases), the reason for which was not explained. The breakdown of admissions by sex, age and vaccination status is shown in the table below.
Notice that a majority of admissions in this period – 57% – had received at least one vaccine dose. An earlier study that I noted before, from the ISARIC4C consortium, had found just 7.3% of hospital admissions over a similar period had received at least one vaccine dose. The reasons for this huge discrepancy are unclear, but given that the earlier figure made headlines for showing how effective the vaccines are, and for the sake of clarity in data, it should be cleared up.
These figures were compared to the vaccine coverage in the population at the time to give the following results in terms of relative risk ratios (“OR” is odds ratio).
These translate to a relative risk reduction of 82% for 70-79 year-olds and 80% for 80+ year-olds after one dose, and 81% for 80+ year-olds after two doses. These are all strangely similar figures when one would expect more differences between the age groups and between being partially and fully vaccinated. It’s not clear the extent to which the declining viral incidence during the study period has been taken into account by the researchers, particularly the fact that the cases among the vaccinated will tend to be from later in the period when viral incidence was lower.