Immunity from Norovirus

by Iain Shaw

Ian Shaw does not work on noroviruses but has a professional interest in that he has worked for the past 10 years on viral immunity.

The range of immunity duration varies very much on which report you read, I have seen ranges from no immunity at all up to 14 weeks (and even one report upto 48 months). Parrino et al (1977) - Clinical immunity in acute gastroenteritis caused by Norwalk agent. N Engl J Med 1977 Jul 297:86-9 showed that there may be 2 different mechanism of immnuity at play, one of short duration, one of much longer duration, and antibody may not be the protective element in all cases as in some challenged volunteers antibody levels did not increase as would be expected.

It does also appear that there may be a genetic contribution to natural resistance to noroviruses, with the ABO blood group system playing a (significant ?) part (3 references below)

  1. Norwalk virus binds to histo-blood group antigens present on gastroduodenal epithelial cells of secretor individuals. Gastroenterology 2002 Jun 122:7 1967-77
  2. Norwalk virus infection and disease is associated with ABO histo- blood group type. J Infect Dis 2002 May 1 185:9 1335-7
  3. A report in preparation - Binding of Norwalk virus-like particles to ABH histo-blood group antigens is blocked by antisera from infected human volunteers or experimentally vaccinated mice. J Virol 2002 Dec 76:12335-43

suggests even further just what blood group antigens are involved.

As to anti-emetics, a lot of the current range of antiemetics are not anti-toxins but rather are inhibitors of the physiological vomiting response, so therefore the effectiveness of antiemetics should not be affected by the mutation of the noroviruses

However, even if we are able to detect the receptor, block it, come up with candidate vaccines etc I really do think that education and awareness of the virus will provide another effective avenue to prevention. Hand washing will have a significant effect on the faecal-oral route of transmission that is without doubt, but the aerosol transmission via vomiting is one that hand washing cannot do anything about (I really love this virus, it is so clever - make someone really sick so they vomit millions of copies around to increase its chance of replication, infectious dose is only 10-100 viral particles).

However if people who were suffering from vomiting and diarrhoea were to exclude themselves from work/school/public areas then a major source of spread would be removed. I know for certain that here in Ireland, in my own workplace people who were actively vomiting carried on working increasing the risk of spread, and those who were sick one day and took the day off work then returned the next day because they felt better, even though they would most likely be shedding the virus for upto 48 hours later through faeces. In fact my wife was ill with gastroenteritis starting on a Monday, was ill until Tuesday lunchtime, a telephone conversation from the doctor suggested she should take the remainder of the week off to break the cycle of infection. When she did return to work she was ridiculed by others who said - 'Yeah I had that on Monday but came back to work the next day' implying that my wife was a slacker and using it as an excuse to take extra time off - I think that in the end in a workplace of 50 people, 10 people (20%) had signs consistent with Norovirus infection, what would that attack rate of been if people had had more consideration ?